Numerous handpieces for rotating tools exist. Turbine driven handpieces are widely used in dental offices and medical labs around the world. Most handpieces include a handle portion, a connector at one end of the handle portion and a tool carries drive head at the other end. The connector provides a connection of the handpiece to various air, water, light and power supply conduits, generally combined in a so called umbilical cord. The drive head houses a tool rotating assembly, generally composed of a tool mount or chuck, and a motor or a turbine turbine, rotatably mounted in the head for driving the chuck.
Various different types of turbine arrangements are in use, all of which include a turbine in a turbine housing, a supply of pressurized air into the housing for driving the turbine and a set of bearings for rotatably supporting the turbine in the housing and the head. Since conventional dental handpieces are constructed to rotate the dental drill or burr at speeds of up to 500,000 rpm, the bearings are subject to large stress. This is exaggerated by the bearings having to additionally support the chuck and tool against the lateral forces applied to the tool during operation. Furthermore, asymmetrical thrust generated by drive air impinging tangentially on the turbine places additional stress on the bearings.
In existing handpieces, mostly ball bearings are used, which generally have a maximum service life of 3 months and must be lubricated each time they are subjected to sterilization conditions. Ceramic bearings have come on the market recently which are more robust and are maintenance free in that they do not need to be lubricated after each sterilization. However, their service life is still not satisfactory.
U.S. Pat. No. 3,906,635 is directed to a dental handpiece with air bearings. In that handpiece, a central spindle supporting the turbine wheel and having an axial, burr receiving bore is supported in the drive head of the handpiece by a pair of cylindrical bearing sleeves which are closely spaced from the spindle, forming a very narrow air passage or air gap therebetween. The bearing sleeves are respectively mounted in a pressure chamber to which pressurized drive air is supplied. The bearing sleeves each include a number of air passages allowing pressurized air to pass from the pressure chamber into the air gap between the spindle and the bearing sleeve. The drive air is supplied simultaneously to the turbine and the air bearings. The pressurized drive air supporting the spindle enters into the bearing chambers, passes through the bearing sleeves and into the air passages, and from there gets exhausted to ambient or into the turbine chamber. It is easily apparent that operating the air bearings and the turbine with the same drive air causes a major disadvantage. At shut down of the drive air, the turbine still rotates while the air pressure is no longer sufficient to fully support the spindle in the bearing sleeves. This can result in serious damage to the bearing, which in turn limits the service life of the turbine drive unit. Moreover, although the cylindrical air cushions may properly support the spindle in radial direction, very little support in axial direction is provided. Axial thrust washers are provided in this prior art construction, which support the spindle in axial direction. Although annular air cushions are provided around the thrust washers, the overall surface of these air cushions appears to be quite small considering the potentially large axial thrust force applied to the spindle upon contact of the burr with a tooth. Furthermore, the sharp angle at the transition from the cylindrical air cushion to the annular air cushion impedes the flow of cushioning air. Thus, an improved bearing design is desired.
Many different air turbine designs and constructions exist, but in common turbine designs drive air is tangentially blown onto the impeller wheel of the turbine and at the circumference of the wheel. The tangential air supply generates asymmetrical thrust and causes asymmetrical loading of the bearings, which increases stress and wear. Furthermore, the torque generation of the turbine is low due to the only localized drive air supply. Moreover, parasitic airflow (drag) is high when the drive air is supplied tangentially at the circumference of the turbine.
Numerous air turbine designs are known in the prior art, wherein a paddle wheel type turbine rotor is driven by drive air impacting onto the turbine vanes at the outer ends thereof and in a direction tangential to the turbine circumference. Representative of the prior art designs are U.S. Pat. No. 6,120,291 and US Patent Application US 2001/0002975. Although U.S. Pat. No. 4,470,813 discloses an air driven turbine arrangement wherein the drive air is somewhat redirected radially before impact onto the turbine wheel, the drive air is still directed onto the turbine vanes in one location and in a generally tangential direction. Thus, a need exists for an improved turbine construction generating higher torque output and less bearing stress.
Prior art chucks of dental handpieces are almost exclusively designed to hold the dental burr by way of a friction fit only. Examples of such constructions are found in U.S. Pat. Nos. 4,595,363, 5,549,474, and 5,275.558. Only low torque transmission is possible between the chuck and the burr in such constructions, higher torque leading to slippage of the burr. In U.S. Pat. No. 6,065,966, a spring loaded pin is used for engaging a recess in a dental tool. However, the use of this arrangement in an air turbine handpiece is not disclosed. In fact, the disclosed arrangement could not be used to hold a dental burr, since the engagement between the pin and the chuck is designed for a non-rotating tool and does not easily lend itself to being used with a rotating tool.
A lock and key type connection is known from U.S. Pat. No. 4,370,132 which teaches the use of a burr with a shank having a flattened end portion at the upper shank end. A dog rigidly connected with the burr receiving sleeve is provided for engagement with the flattened end of the burr shank. The burr cannot be fully inserted into the chuck until the burr end fits into the dog, so that the burr must be turned relative to the chuck until these interlocking portions align. It is a disadvantage of this prior art arrangement that the burr must be rotated in the chuck until the lock and key structures fit together. Since the chuck also provides a friction fit with the burr, rotating the almost completely inserted burr within the chuck would necessitate some kind of mechanism which keeps the chuck from rotating in the drive head, or the burr must be repeatedly removed and reinserted in a slightly different angular position. Locating the interlocking mechanism deep in the drive head of the handpiece makes it impossible for the user to visually pre-align the lock and key structure prior to insertion of the burr. Thus, insertion of the burr is an exercise of trial and error.
Dental handpiece air turbines are normally shut down by simply stopping the supply of pressurized drive air. However, since the turbine is rotating at high speed, it takes some time to gradually slow down and come to a stop. This is undesirable, since for safety reasons, the dentist must wait until the turbine has fully stopped before removing the handpiece from a patient's mouth. Furthermore, during this so called rundown period, the continued rotation of the turbine generates a vacuum in the turbine chamber which may lead to contaminants being sucked into the chamber.
U.S. Pat. No. 5,507,642 discloses a discharge air shut-off arrangement for a dental handpiece turbine unit, which automatically prevents the flow of discharge air through the lower bearing during rundown of the turbine in order to prevent the generation of a vacuum. This is achieved by using a flexible Belleville washer which is held in a flat configuration by the drive air and automatically curves upward when the drive air is shut off, thereby closing off the air discharge passage. U.S. Pat. No. 5,782,634 discloses an auto-stop arrangement which includes a valve in the exhaust air conduit which is operated by the drive air pressure and closes the exhaust air conduit when the drive air pressure falls below a certain level. However, the valve arrangements of these two patents shut off only the exhaust air conduit, not the drive air and chip air/water conduits. Thus, a vacuum may still be generated and contamination may still occur. Consequently, a mechanism is desired which provides for a reliable and quick stopping of the turbine and prevents contamination of the turbine chamber as much as possible.
Dental turbine handpieces generally include either a straight neck or a bent neck, the latter intended to facilitate access to the back of a patient's teeth. However, the tooth clearance achievable with such a construction is limited by the length of the burr. For some situations, a better tooth clearance is desired. Furthermore, the treatment field is usually partially obstructed during use by the drive head and the neck. U.S. Pat. Nos. 1,984,663 and 4,820,154 respectively disclose a dental handpiece with an adjustable neck angle and a dental instrument (scaler) with a neck portion including two bends. Thus, a handpiece neck portion design is desired which provides additional tooth clearance and improved visibility of the field of treatment.
As mentioned, fluids and power are supplied to dental handpieces by way of an umbilical cord normally removably connected thereto at a rear end. The connection is usually achieved by an umbilical cord swivel connection which prevents a tangling of the cord. However, this connection normally extends straight in extension of the handpiece, which places a fairly high twisting strain on the wrist of the user, since the straight swivel connection combined with the inherent rigidity of the umbilical cord acts as a sort of lever which exaggerates the actual downward force created by the weight of the cord. This problem has plagued dentists for years with no solution for dental handpieces being available. Various swivel connectors are known in the art for releasable connection of a dental handpiece to the umbilical cord including the working fluid supply and fiberoptic conduits. Examples of swivel connectors are shown in U.S. Pat. Nos. 5,057,015, 6,033,220 and 6,319,003. However, all of these connectors provide only a straight connection between the umbilical cord and the handpiece. Thus, a need exists for a connector which reduces wrist strain.